Tuning the Bi³⁺-photoemission color over the entire visible region by manipulating secondary cations modulation in the ScV_xP_1-xO₄:Bi³⁺ (0 ≤ x ≤ 1) solid solution

Unlike rare earth (RE) (e.g., Eu²⁺) and non-RE (e.g., Mn²⁺) doped tunable solid solutions that frequently suffer from the visible re-absorption issue, the Bi³⁺ ion features the remarkable advantages of a strong UV excitation intensity and an excitation tail of less than 430 nm, giving Bi³⁺ a strong potential to solve the re-absorption issue for future lighting technology. Herein, we report a type of zircon-type ScV_xP_1-xO₄:Bi³⁺ (0 ≤ x ≤ 1) emission-tunable solid solution that has a strong UV excitation intensity yet no significant light absorption. We reveal that gradual substitution of larger V ions for smaller P ions, which means expansion of the lattice cell, can shift the excitation edge from 295 to 385 nm, the excitation tail from 340 to 425 nm and emission position from 455 to 641 nm, without causing a large change to the Stokes shift. This spectral shifting is found to be a consequence of the complex dependence of the intra-ion and charge-transfer related transitions of Bi³⁺ with the crystal structure. Owing to the remarkable excitation-triggered multi-emission properties, we then discover that the ScV_xP_1-xO₄:Bi³⁺ solid solution can serve as a type of potential material for anti-counterfeiting and information protection applications. This work can provide design insights into discovering more RE and non-RE doped tunable solid solutions in the future, through modulation of the secondary cations in the isostructural crystals.